A husband-and-wife research team from the University of Pennsylvania School of Medicine reports that the relative size of the sections of the brain that constrain aggression and monitor behavior are larger in women than in men.
Conversely, the researchers say they also found that the sections of the brain that promote aggression are smaller in women than in men.
Ruben C. Gur and Raquel E. Gur, reporting in the September issue of Cerebral Cortex, say these are biological characteristics that translate into important behavioral distinctions between the sexes.
"Perhaps the greatest emotional difference between men and women is their expression of aggression," says Ruben Gur, a professor at the school's department of psychiatry, neurology and radiology.
"This study provides neurobiological evidence that women have more of the brain tissue that's used censoring aggressive and angry responses, while men have more brain tissue of the type that initiates aggression and impulsive, angry responses," he adds.
The Gurs say their research was based on established scientific knowledge that emotional control and expression are linked to specific regions of the human brain. The so-called limbic system, particularly the amygdala, for instance, is involved in the emotional behavior associated with arousal and excitement, and the orbital frontal region is involved in the modulation or control of aggression.
When their team performed MRI scans on the brains of 116 healthy men and women, they found the 59 women in their study had a significantly higher volume of brain tissue in the orbital frontal region in proportion to amygdala brain tissue volume than did the 57 men they examined.
This, they conclude, gives women an advantage when it comes to controlling their aggressive behaviors. Men, it would seem, are biologically fated to be more hot-headed than women.
Kenneth Goldberg, a clinical assistant professor of neuropsychology at Widener University in Pennsylvania, says research findings like these can be helpful in understanding differences between male and female behavior.
"Some people don't want to admit that men's and women's brains are different," says Goldberg. "Even though research studies like this one show that such differences do exist and are quantifiable, there are those who insist that biology doesn't play a role in human behavior. Obviously, brain-size differences between males and females do exist and may prove to be very important."
Goldberg points out that understanding what goes into the expression of aggression at the biological level is also relevant and valuable.
"The Gurs' results provide us with a way to conceptualize the physiological mechanisms that play a role in specific human behaviors, such as violence and aggression," Goldberg says. "Although the field of science isn't there yet, one day information of this type can help in the development of treatment and prevention approaches."
According to Ruben Gur, the next step in the research is to examine the role of individual differences in the context of the male-female brain biology the research team documented.
"We will now be looking at how the proportion of brain tissue promoting aggression to that modulating aggression relates to the way specific men and women express aggression," he says. "We are hoping to determine whether it is feasible to use MRI scans as an anatomic index to predict the risk of aggression in certain individuals."
"If high-risk individuals can be identified based on the relative size of some of these parts of their brains, it may be possible to develop means for them to enhance the brain tissue that inhibits or controls these aggressive emotions and their expression," he says.
What To Do